The invention relates to a capacitor winding apparatus and method and more particularly to an apparatus and method of winding a dry metallized plastic film capacitor.
Capacitor winding machines, even those for winding a dry metallized plastic film capacitor, are well known in the art. Typically, two supply rolls of the metallized plastic film are mounted on separate spindles that are located at a remote distance from the drive means for a capacitor core. The plastic films travel over idlers and/or drive rollers and/or stationary surfaces before being wound onto the core to form the capacitor. These rollers and/or stationary surfaces are disadvantageous insofar as they can cause damaging scratches in the metallized plastic film surfaces which would result in a poor quality capacitor. In most machines, separate motors are used to drive each of the supply rolls and an additional motor is used to rotate the spindle on which the core is mounted. Since most of the metallized plastic films are extremely thin and hard to handle, means must be provided to maintain a constant tension on the supply of film to prevent misalignment of the winding. In the prior art devices, this has usually comprised a dancer roller which bears against the film, the dancer roller being connected to a potentiometer. A momentary increase or decrease in the film tension changes the position of the potentiometer and, consequently, adjusts the speed of the drive motors on the plastic film supply roll spindles.
Several machines currently available have the capability of winding capacitors on plastic cores which remain within the completed capacitor (known as the "lost core" process). These winding machines are all similar in design and consist of a complicated revolvable turret with three winding spindles located 120 degrees apart. In the first position, a plastic core is positioned on the spindle; in the second position, the winding is made; and, in the third position, the finished winding is removed from the apparatus.
All of these machines have elaborate mechanisms to cut, fold or otherwise separate the cut ends of the plastic films so as to stagger them at the beginning and the end of the winding. Alignment of the edges of the plastic film during the winding is accomplished by passing the plastic film over one or move idler rollers and the application of a constant tension to reduce the side slip or run out. In most of the prior art machines, adjustment and control of the run out or side slip is an extremely sensitive adjustment and results in a great deal of lost production time in setting up the apparatus and in readjusting the amount of run out to acceptable levels.
Many of the existing machines apply a pressure idler roll throughout the winding at or near the point of tangency where the two plastic films make contact with the core. This is an attempt to minimize the thin air layer on the plastic film that would normally enter the winding, by pinching the air from the film surface just before the wind-up occurs. However, with plastic films, such as polypropylene, that tend to adhere very tightly when positioned closely to each other, air will become trapped just before the plastic films reach the pressure roller. Because of the tenacity of this adhesion, only a portion of this trapped air can be excluded from the winding by the single pressure roller acting on the two layers of plastic film. This air film, should it enter the winding, would cause air voids in the completed capacitor in which corona discharges would occur, and would also provide sufficient lubrication to cause the film to side slip during the winding operation.
Control of the plastic film tension on all of the known winding machines is also aggravated during acceleration and deceleration of the winding because of the moment of inertia of the supply rolls, especially when new supply rolls are added. This problem has limited the diameter of the supply rolls to approximately ten inches on even the best of the controlled tension winding machines.
Typical prior art coil winding machines are disclosed in the following U.S. patents:
______________________________________ 3,227,388 Masini 3,425,641 Gallet et al 3,473,750 Bayard, Jr. 3,540,099 Perrenound ______________________________________
Masini describes a coil winding machine wherein a foil is passed between spaced apart, pressure sensitive terminal tapes which, at intervals, are moved into contact with the opposite surfaces of the metal foil to adhere thereto over short distances. The metal foil to which the terminal tape has been applied is then would upon a core with a paper coil.
Gallet et al discloses an apparatus for winding capacitors utilizing metallized film supply rolls mounted on pivoted arms that are spring biased into tangential contact with the core, but no means are shown to move the supply rolls out of contact with the core. Bayard, Jr. is directed to an apparatus for winding capacitors utilizing metallized film supply rolls which feed the metallized film from each in superposed relation to a split arbor. There is also included means for interposing an insulating ribbon between the metallized films near the end of one winding and at the beginning of the next successive winding.
Perrenoud is directed to a machine for making electric condensers wherein a plurality (three) of core grippers are mounted on a turret which rotates each core gripper from one of three working positions to another. In a first working position, the core gripper releasably grips a core. In the second working position strips of material are wound onto the core. In the third working position, the strips of material are severed and a protective band is applied around the material wound on the core.
The following patents also illustrate typical prior art coil winding devices on individual features utilized thereon:
______________________________________ 3,367,594 3,779,474 3,641,640 3,073,008 3,278,130 1,385,379 3,163,347 3,273,816 3,104,073 3,201,056 3,459,616 British Pat. 669,264 3,815,188 Canadian Pat. 644,196 3,689,002 French Pat. 1,279,766 ______________________________________